Superconductor coplanar waveguide

Abstract

A lanthanum aluminate (LaAlO 3 ) substrate on which thin films of layered perovskite copper oxide superconductors are formed. Lanthanum aluminate, with a pseudo-cubic perovskite crystal structure, has a crystal structure and lattice constant that closely match the crystal structures and lattice constants of the layered perovskite superconductors. Therefore, it promotes epitaxial film growth of the superconductors, with the crystals being oriented in the proper direction for good superconductive electrical properties, such as a high critical current density. In addition, LaAlO 3 has good high frequency properties, such as a low loss tangent and low dielectric constant at superconductive temperatures. Finally, lanthanum aluminate does not significantly interact with the superconductors. Lanthanum aluminate can also be used to form thin insulating films between the superconductor layers, which allows for the fabrication of a wide variety of superconductor circuit elements.

We claim:  
     
       1. A superconductor coplanar waveguide comprising: 
       (a) a lanthanum aluminate substrate; and  
       (b) at least one superconductor film on the lanthanum aluminate substrate.  
     
     
       2. The coplanar waveguide of  claim 1 , wherein the superconductor film comprises first, second and third films, the first film forming the conductor of the waveguide and being disposed between the second and third films, and the second and third films forming the walls of the waveguide. 
     
     
       3. The coplanar waveguide of  claim 2 , wherein the width of the first superconductor film is substantially narrower than the width of the second and third superconductor films. 
     
     
       4. The coplanar waveguide of  claim 1 , wherein the superconductor film has a crystalline structure that is substantially oriented to the crystalline structure of the lanthanum aluminate substrate. 
     
     
       5. The coplanar waveguide of  claim 1 , wherein the superconductor film has a crystalline structure and lattice constant that substantially match the crystalline structure and lattice constant of the lanthanum aluminate substrate. 
     
     
       6. The coplanar waveguide of  claim 1 , wherein the superconductor film has a perovskite structure. 
     
     
       7. The waveguide of  claim 6  wherein the superconductor film has a layered perovskite structure. 
     
     
       8. The coplanar waveguide of  claim 1 , wherein the lanthanum aluminate substrate has a lattice constant ranging from about 3.80 to about 3.85 Å. 
     
     
       9. The coplanar waveguide of  claim 1 , wherein the superconductor film is selected from the group consisting of (i) RBaCuO compounds, where R is a rare earth element or yttrium, and (ii) copper oxide compounds comprising metallic elements, wherein at least one of the metallic elements is selected from the group consisting of bismuth and thallium. 
     
     
       10. The coplanar waveguide of  claim 1 , wherein the superconductor film comprises barium, copper, oxygen, and an element selected from the group consisting of yttrium, erbium, lanthanum, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, thulium, ytterbium, lutetium, and thallium. 
     
     
       11. The coplanar waveguide of  claim 1 , wherein the superconductor film comprises (i) calcium, (ii) copper, (iii) oxygen, (iv) an element selected from the group consisting of barium and strontium, and (v) an element selected from the group consisting of thallium and bismuth. 
     
     
       12. The coplanar waveguide of  claim 2 , wherein the superconductor film is formed on the substrate at a temperature of at least about 700° C., and wherein there is substantially no chemical interaction between the superconductor film and the substrate. 
     
     
       13. The coplanar waveguide of  claim 1 , wherein the superconductor film has a perovskite crystalline structure. 
     
     
       14. A superconductor coplanar waveguide comprising: 
       (a) a lanthanum aluminate substrate; and  
       (b) at least one superconductor film on the lanthanum aluminate substrate, the superconductor film capable of exhibiting superconductive electrical properties at temperatures maintainable with liquid nitrogen.  
     
     
       15. A superconductor coplanar waveguide comprising: 
       (a) a substrate of lanthanum aluminate; and  
       (b) first, second and third superconductor films on the substrate, the first film forming the conductor of the waveguide and being disposed between the second and third films, and the second and third films forming the walls of the waveguide.  
     
     
       16. A superconductor coplanar waveguide comprising: 
       (a) a substrate of lanthanum aluminate having a first perovskite crystalline structure; and  
       (b) first, second and third superconductor films on the substrate, the first film forming the conductor of the waveguide and being disposed between the second and third films, and the second and third films forming the walls of the waveguide,  
       wherein the first, second and third superconductor films have a second perovskite structure that is substantially oriented to the first perovskite structure of the substrate so that the superconductor films exhibit superconductive electrical properties at temperatures maintainable with liquid nitrogen.  
     
     
       17. In a superconductor coplanar waveguide in which at least one superconductor film is on a substrate, the improvement being the substrate comprises lanthanum aluminate. 
     
     
       18. The superconductor coplanar waveguide of  claim 17 , wherein the substrate and the superconductor film both have perovskite crystalline structures that are substantially oriented to one another. 
     
     
       19. The superconductor coplanar waveguide of  claim 17 , wherein the superconductor film has a crystalline structure and a lattice constant and the lanthanum aluminate substrate has a crystalline structure and a lattice constant that substantially matches the crystalline structure and the lattice constant of the superconductor film. 
     
     
       20. The waveguide of  claim 17  wherein the superconductor film comprises erbium barium copper oxide superconductor deposited on the substrate. 
     
     
       21. The waveguide of  claim 17  wherein the superconductor film comprises yttrium barium copper oxide superconductor deposited on the substrate. 
     
     
       22. The waveguide of  claim 17  wherein the superconductor film comprises strontium, calcium, copper, oxygen, and an element selected from the group consisting of thallium and bismuth. 
     
     
       23. The waveguide of  claim 17  wherein the superconductor film comprises barium, calcium, copper, oxygen, and thallium. 
     
     
       24. In a superconductor coplanar waveguide in which at least one superconductor film is on a substrate, the improvement being the substrate consists essentially of lanthanum aluminate having a crystalline structure and a lattice constant that substantially matches the crystalline structure and the lattice constant of the superconductor film, and wherein the crystalline structures are substantially oriented to one another, and there is substantially no chemical interaction between the superconductor film and the substrate. 
     
     
       25. A superconductor coplanar waveguide comprising: 
       (a) a lanthanum aluminate substrate; and  
       (b) at least one superconductor film on the lanthanum aluminate substrate, the superconductor film comprising copper and oxygen.  
     
     
       26. A superconductor coplanar waveguide comprising: 
       (a) a lanthanum aluminate substrate; and  
       (b) at least one superconductor film on the lanthanum aluminate substrate, the superconductor film comprising copper and oxygen and the superconductor film capable of exhibiting superconductive electrical properties above the temperature of liquid nitrogen.  
     
     
       27. A superconductor coplanar waveguide comprising: 
       (a) a substrate of lanthanum aluminate; and  
       (b) at least one superconductor film comprising copper and oxygen on the substrate, the superconductor film (i) having a crystalline structure that substantially matches, and is substantially oriented to, the crystalline structure of the substrate, and (ii) having substantially no chemical interaction with the substrate.  
     
     
       28. A superconductor coplanar waveguide comprising: 
       (a) a substrate of lanthanum aluminate; and  
       (b) at least one superconductor film comprising copper and oxygen on the substrate, the superconductor film (i) capable of exhibiting superconductive electrical properties maintainable with liquid above the temperature of liquid nitrogen, (ii) having a crystalline structure that matches, and is substantially oriented to, the crystalline structure of the substrate, (iii) having a lattice constant that substantially matches the lattice constant of the substrate, and (iv) having substantially no chemical interaction with the substrate.  
     
     
       29. A superconductor coplanar waveguide comprising: 
       (a) a substrate of lanthanum aluminate having a first perovskite crystalline structure; and  
       (b) at least one superconductor film comprising copper and oxygen on the substrate; the superconductor film (i) having a second perovskite structure that is substantially oriented to the first perovskite crystalline structure of the substrate; and (ii) having substantially no chemical interaction with the substrate,  
       whereby the superconductor film on the substrate exhibits superconductive electrical properties above the temperature of liquid nitrogen.  
     
     
       30. The superconductor coplanar waveguide of any one of claims  25  or  27  wherein the superconductor film has superconductive electrical properties above the temperature of liquid nitrogen. 
     
     
       31. The superconductor coplanar waveguide of any one of claims  25  or  26  wherein the superconductor film has a crystalline structure that is substantially oriented to the crystalline structure of the lanthanum aluminate substrate. 
     
     
       32. The superconductor coplanar waveguide of any one of claims  25  or  26  or  29  wherein the superconductor film has a crystalline structure and lattice constant that substantially match the crystalline structure and lattice constant of the lanthanum aluminate substrate. 
     
     
       33. The superconductor coplanar waveguide of any one of claims  25 ,  26 ,  27 ,  28  or  29  wherein the superconductor film has a layered perovskite structure. 
     
     
       34. The superconductor coplanar waveguide of any one of claims  25 ,  26 ,  27 ,  28 , or  29  wherein the lanthanum aluminate substrate has a lattice constant ranging from about 3.80 to about 3.85 Å. 
     
     
       35. A superconductor coplanar waveguide comprising: 
       (a) a substrate of lanthanum aluminate; and  
       (b) first, second and third superconductor films on the substrate, the first film forming the conductor of the waveguide and being disposed between the second and third film, and the second and third films forming the walls of the waveguide, wherein the superconductor films comprise barium, copper, oxygen, and an element selected from the group consisting of yttrium, erbium, lanthanum, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, thulium, ytterbium, lutetium, and thallium.  
     
     
       36. A superconductor coplanar waveguide comprising: 
       (a) a substrate of lanthanum aluminate; and  
       (b) first, second and third superconductor films on the substrate, the first film forming the conductor of the waveguide and being disposed between the second and third films, and the second and third films forming the walls of the waveguide, wherein the superconductor films comprise (i) calcium, (ii) copper, (iii) oxygen, (iv) an element selected from the group consisting of barium and strontium, and (v) an element selected from the group consisting of thallium and bismuth.